The present invention relates to an aqueous polymeric composition for use in the manufacture of pressed lignocellulose hardboard sheets. The composition improves the surface characteristics of the hardboard sheets and provides for a quick release of stacked pressed hardboard sheets from interlineated platens during the pressure and heat curing of the sheet in the hydraulic press operation, thus producing a smooth finished pressed surface for each of the hardboard sheets. The finished surface of the hardboard sheets provides for improved paint holdout, a smooth hard surface, improved water resistance, board strength and fiber retention, as well as other desirable physical characteristics.
In the manufacture of hardboard, the sheets having two opposite smooth surfaces are produced from wet felted lignocellulosic fibers which are consolidated under pressure in a press to density of about 31 pounds per cubic foot or greater. The hardboard sheets are formed in their early stages of development from the hydrolyzed felted lignocellulosic fibers that have been felted into wet lap sheets. The wet lap sheets are stacked in a hydraulic press with a platen capable of being heated such as by steam between wet lap sheets. The wet lap sheets are dried to contain little residual moisture while being maintained under a consolidating pressure by maintaining the press under pressure and the platens heated to drive off the moisture.
After the consolidation operation is complete, the pressure on the sheets is released and the stacked consolidated sheets are in the form of finished hardboard sheets having opposite hard smooth surfaces.
One of the problems experienced after the pressing operation is the sticking of the hardboard sheets to the caul or platen of the press. Various approaches have been used to provide for a quick and positive release of the surface of the sheets from the platens, such as by applying to the surface of the lap sheet before consolidation various surface treatments such as water spray, talcum powder, water-soluble melamine copolymers, vinyl acetate copolymer emulsions and like treatments.
While such surface treatments have helped to mitigate the problem, the sticking of hardboard sheets to the caul or platen during manufacture still exists, with the result that considerable press downtime is experienced which, of course, decreases the rate of production with resulting increase in the cost of each finished hardboard sheet product. Other disadvantages experienced in the production of hardboard sheets that detract from high quality are fiber pickup, lack of good water repellency, and a high degree of water absorption, all of which must be improved if the production of high quality hardboard sheet at a reasonable cost is to be accomplished.